Wideband Electromagnetic Research Articles

Enhanced Electromagnetic Wave Absorption in W-Type Ba-Hexaferrites: Role of Composition and Grain Growth

W-type Ba-hexaferrite, BaZn2−xCoxFe16O27, was synthesized via both conventional solid-state (x = 0.4, 0.5, 0.6, 0.75, 1.0, 1.25, 1.5) and molten-salt methods (x = 0.75, 1.0, 1.25). The structure, electromagnetic (EM) properties, and EM wave absorption characteristics were examined across a frequency range of 0.1–18 GHz, focusing on the influence of varying x. As x increased from 0.4 to 0.75, the magnetic anisotropy field (Hani) decreased, reaching its minimum at x = 0.75, before rising again as x continued to increase up to 1.5. Hani was found to be proportional to the ferromagnetic resonance (FMR) frequency, allowing for the tuning of the EM wave absorption frequency range. W-type hexaferrite–epoxy composites (10 wt%) with x values between 0.6 and 1.5 exhibited outstanding wideband EM wave absorption, with a maximum absorption (RLmin < −50 dB) and a wide absorption bandwidth where RL < −10 dB extended beyond 10 GHz (Δfwb > 10 GHz). The x = 1.25 sample with a thickness of 2.37 mm achieved RLmin = −69 dB at 7.8 GHz, while the x = 1.0 sample with a thickness of 2.33 mm delivered Δfwb = 12.5 GHz (5.1–17.6 GHz). Samples synthesized via the molten-salt method showed larger plate-like grain growth compared to those produced by the solid-state method, with permeability spectra shifting to lower frequencies, consequently lowering the EM wave absorption band.

Synchronously Formed Hetero- and Hollow Core-Branch Nanostructure Toward Wideband Electromagnetic Wave Absorption.

The intrinsic limitation of low electrical conductivity of MoSe2 resulted in inferior dielectric properties, which restricts its electromagnetic wave absorption (EMWA) performances. Herein, a bimetallic selenide of MoSe2/CoSe2@N-doped carbon (NC) composites with hollow core-branch nanostructures are synthesized via the selenization treatment of MoO3 nanorods coated with ZIF-67. By adjusting the mass ratio of ZIF-67 to MoO3, the electromagnetic parameters and morphologies of composites are finely tuned, further ameliorating the impedance matching and EMWA performances. The involvement of NC improves the electronic conductivity of the composites. The synchronously formed heterostructure not only facilitates charge transfer but also leads to the accumulation and uneven distribution of charges, thus enhancing the conductive loss and polarization loss. The hollow core-branch nanostructure provides abundant conductive networks, heterointerfaces, and voids, significantly enhancing the EMWA property. Density functional theory implies that the heterostructures effectively boost charge transport and change charge distribution, which heightens the conductive loss and polarization loss. As a result, the composites demonstrate a minimum reflection loss value of -53.53 dB at 9.04 GHz, alongside a maximum effective absorption bandwidth of 6.32 GHz. This work offers invaluable insights into novel structural designs for future research and applications.

Thermally Conductive Phase Change Composites for Wideband Electromagnetic Noise Reduction and Thermal Management

Thermally Conductive Phase Change Composites for Wideband Electromagnetic Noise Reduction and Thermal Management

A Hybrid Forward-Inverse Neural Network With the Transceiver-Configuration-Independent Technique for the Wideband Electromagnetic Inverse Scattering Problem

A Hybrid Forward-Inverse Neural Network With the Transceiver-Configuration-Independent Technique for the Wideband Electromagnetic Inverse Scattering Problem

Anti-reflection metasurface synergizing plasma and lattice modes: an efficient route to wideband electromagnetic transparency under extreme angles

All-angle wideband electromagnetic (EM) transparency for dual polarizations is desired for many practical applications. Conventionally, surface-mount anti-reflection materials or films are usually used to reduce the reflection and thus enhance transparency. In this paper, we propose to achieve wideband EM transparency under extreme angles for both TE- and TM-polarizations using embedded anti-reflection metasurface. The metasurface is composed of a pair of long and short metallic strips, which can introduce both plasma and lattice modes into the original half-wave wall. The plasma mode can create an angle-stable transmission peak at a lower frequency while the lattice mode renders a transmission peak under extreme angles at a higher frequency due to scattering cancellation between short strips and the substrate. By synergizing the plasma, half-wave, and lattice modes consecutively, wide-band transparency can be achieved under extreme angles for TE polarization. Due to the anisotropy of the metasurface, wideband transparency under TM-polarization is maintained. This finally enables us to obtain wideband EM transparency for dual polarizations under extreme angles. More importantly, the metasurface can also be customized to operate best under any given incident angle. Prototypes were designed, fabricated, and measured. Both the simulation and experiment results verify our method. This work provides an efficient route to wideband EM transparency under extreme angles and may find wide applications in communication, radar, and others.

Estimating Parameters of Ballistic Target by Single Hybrid Radar Based on Vortex and Wideband Electromagnetic Waves

Estimating Parameters of Ballistic Target by Single Hybrid Radar Based on Vortex and Wideband Electromagnetic Waves

Dispersion-boosting wideband electromagnetic transparency under extreme angles for TE-polarized waves.

Half-wave wall is the most common method of achieving electromagnetic (EM) transparency. Transmission windows can be formed when reflected waves are out of phase. Due to the interference mechanism, these windows are dependent on the frequency and incident angle of EM waves, leading to limited bandwidth, especially under extreme angles. In this letter, we propose to extend the bandwidth of the transmission window under extreme angles by utilizing dispersion. To this end, long metallic wires are embedded into the half-wave wall matrix, without increasing the physical thickness. Due to the plasma-like behavior of metallic wires under TE-polarization, the effective permittivity of the half-wave wall, rather than keeping constant, increases with frequency nonlinearly. Such a dispersion will boost wideband transparency in two aspects. On one hand, an additional transmission window will be generated where the effective permittivity equals that of the air; on the other hand, the 1st- and 2nd-order half-wave windows will be made quite closer. By tailoring the dispersion, the three windows can be merged to enable wideband transparency under extreme incident angles. A proof-of-principle prototype was designed, fabricated, and measured to verify this strategy. Both simulated and measured results show that the prototype can operate in the whole Ku-band under incident angle [70°, 85°] for TE-polarized waves. This work provides an effective method of achieving wideband EM transparency under extreme angles and may find applications in radar, communications, and others.

Tunable and broad-band electromagnetic wave absorption using W-type Hexaferrites in 1–40 GHz range

W-type Sr-hexaferrites, Sr0.75Ca0.25Zn2-xCoxFe16O27 (0.0 ≤ x ≤ 2.0), were synthesized, and their magnetic and electromagnetic (EM) wave absorption properties were investigated. As x increased from 0.0 to 2.0, the saturation magnetization value increased and reached a maximum at x = 1.25, followed by a decrease, while the magnetic anisotropic field (Hani) decreased and showed a minimum at x = 1.0, then increased again. The variation in Hani could be controlled by adjusting the value of x, which also changed the ferromagnetic resonance (FMR) frequency and enabled control over the frequency band of EM wave absorption. It is demonstrated that the EM wave absorption is primarily controlled by imaginary part of permeability (μ") induced by FMR. Composite of the W-type hexaferrite-epoxy (10 wt%) with x = 0.75–2.0 showed a broad-band EM wave absorption in the 1–18 GHz range, while the composites with x = 0–0.4 showed it in the 26.5–40 GHz. The x = 1.25 sample satisfied RL < − 10 dB in the 7–17 GHz range with a thickness of 2.1 mm, while x = 0.3 sample satisfied RL < − 10 dB in the 27–39 GHz with a thickness of 0.8 mm. Sr0.75Ca0.25Zn2-xCoxW is a very promising material for tunable wideband EM wave absorbers in 1–40 GHz range.

Silicon-coated fibrous network of carbon nanotube/iron towards stable and wideband electromagnetic wave absorption

• A novel multi-dimensions of core-shell structure by immersing the highly fibrous CNT−Fe structure into solid-state silicon (SiO 2 ) matrix has been designed using the stale SiO 2 as the outmost shell. • Structural-evolution towards the wideband EM absorption has been step-by-step discussion. • The SiO 2 -coated CNT-Fe structures exhibit good stability against air-induced oxidation and acid corrosion while maintaining high EM absorption. • our work elevates the utility of EM absorbers to real-world applications such as anti-acid and oxidation ability. Materials that can absorb electromagnetic (EM) wave have garnered increased attention in recent years due to their potential to mitigate the ever increasing environmental pollution by EM waves. Thanks to recent advances in micro/nanofabrication, a variety of magnetic metal-based EM absorbers have been reported. The design and synthesis of EM absorbers that exhibit efficient and wide-band absorption at small thicknesses, however, remains elusive. Here we report the design of fibrous nanostructures consisting of magnetic iron (Fe) nanoparticles and carbon nanotubes (CNTs), which exhibits a wide-band EM absorption (3.8 GHz) while maintain the thickness at 1.2 mm. In our work, we created a novel core-shell structure by immersing the highly fibrous CNT−Fe structure into solid-state silicon (SiO 2 ) matrix. Finally, the SiO 2 -coated CNT−Fe structures exhibit good stability against air-induced oxidation and acid corrosion while maintaining high EM absorption. Overall, the results reported in this study present new avenues to absorb EM from ambient air. We believe that our work elevates the utility of EM absorbers to real-world applications such as anti-acid and oxidation ability.

Influence of Spatial Correlation Function on Characteristics of Wideband Electromagnetic Wave Absorbers with Chaotic Surface

Electromagnetic metasurface with chaos patterned surface could bring rich interaction modes contributing to fully disordered random motions in deterministic systems, which preform uncertainty, irreducibility and unpredictability. We investigate the influence of the correlation function (CF) properties of surface random patterns on the wave absorption performance. The complicated correlation function provides a fully developed random state, broadening the absorption bandwidth significantly and is helpful for reaching higher absorption rate. With the increasing number of peaks in the correlation function, the absorption band at –15 dB reflectivity widens significantly, band at –20 dB reflectivity begins to emerge. As the first peak’s distance from the original point in the CF is enlarged, the absorption trough is gradually formed and deepened to –35 dB level. The results give in-depth understanding of the relation between absorption behavior and controlling parameters including correlation, image information and foam spacer layer thickness. This high absorption absorber has great application potential in customizable radio communication compatibility device and anechoic testing chamber.

An angle-insensitive electromagnetic absorber enabling a wideband absorption

· This work shows the relationship between the orientation of micro-/nanostructures of the EM absorbers and the associated EM parameters. · A mechanism to describe the underlying mechanism behind the EM incident angle sensitivity of the EM absorbers is proposed in this work. · The proposed mechanism guided the development of a novel class of EM absorbers with wide-angle, high-performance EM absorption. · A graphitized carbon nanospheres derived from bamboo exhibit angle-insensitive and wideband EM absorption performance with an effective absorption band up to 3.5 GHz under a thickness of 1.4 mm only. Electromagnetic (EM) wave absorbers with wideband absorption capability are proposed as a strategy to mitigate environmental pollution by EM waves. However, designing an EM absorber with its performance capacity independent of the EM wave incident angle remains elusive to date. Resolving this challenge requires development of EM absorbers whose EM absorption performance is insensitive to the EM wave incident angle. Herein, we synthesized EM absorbers with a variety of structures with different symmetries (including micro-/nanospheres, nanoflakes and nanotubes) to study the effect of the EM absorbers' structure and the EM wave incident angle on the EM absorption performance. Our analysis reveals that non-magnetic EM absorbers with spatially symmetric nanostructures exhibit excellent EM wave incident angle-insensitivity. Finally, we demonstrate that a class of non-magnetic EM absorbers made from bamboo derived-carbon nanospheres exhibit EM incident angle-insensitivity and wideband EM absorption performance with an effective absorption band up to 3.5 GHz when the thickness is 1.4 mm, a significant improvement from prior studies which used thicknesses as high as 3–4 mm for comparable EM absorption performance.

Graphene Based Wideband Electromagnetic Absorbing Textiles at Microwave Bands

The design and realization of graphene based wideband electromagnetic (EM) absorbing textiles are becoming of primary interest. Hence, the development of new conductive coatings to be cast onto commercial textiles is crucial. In this article, we propose new graphene based absorbing textiles that conjugate outstanding EM absorbing properties at radiofrequency with low-weight, flexibility, cost-effectiveness, and washability. With this purpose, an innovative production process of polyvinylidene fluoride (PVDF) coatings filled with graphene nanoplatelets (GNPs) is developed for the production of radar-absorbing coated textiles, which are fully characterized in terms of morphological, electrical, and EM absorbing properties. In particular, the complex dielectric permittivity of the coated textiles including different amounts of GNPs is assessed through the measurement of the complex permittivity of a benchmark sample, the consequent estimation of the average GNP size and the prediction by simulations of the effective complex permittivity of graphene based coatings loaded with different GNP amounts. Such predicted data are crucial to design radar absorbing textiles with minimum bandwidths at −10 dB of 5 GHz and reflection coefficients below −5 dB over all the frequency range from 8 up to 18 GHz. These textiles are then produced and characterized in terms of reflection coefficient in free space against a plane wave with normal incidence. The obtained results demonstrate the full satisfaction of the design requirements. In fact, the produced samples show a reflection coefficient with a bandwidth at −10 dB up to 77% of the resonant frequency.

Wideband, polarization independent electromagnetic wave absorber using cross arrow resonator and lumped SMD resistors for C and X band applications

In this work, a polarization independent and wideband electromagnetic (EM) waves absorbing frequency selective surface (FSS) structure is presented. The unit cell of the proposed FSS consists of an assembly of cross arrow resonators with four SMD resistors mounted on it, to enhance the absorbance bandwidth. This unit cell also possesses a four-fold symmetry which makes it polarization insensitive. The designed unit cell is compact with the length and width dimensions as 0.19λL × 0.19λL, and thickness of 0.13λL, where λL is the guided wavelength corresponding to the lowest operating frequency. The proposed absorber is theoretically and experimentally tested for its absorbance, cross-polarization level, and radar cross section (RCS) characteristics. The computer-aided simulation and practical measurements indicate that the proposed absorber offers more than 90% (with a fractional bandwidth of 93%) absorbance for normal incidence at 4.5–12.4 GHz frequency band. The cross-polarization reflection coefficient analysis indicates that the proposed FSS configuration behaves as an absorber and not a polarization convertor. The input impedance plot, surface current distribution, and E-field distribution of the unit cell were also analyzed and presented to understand the absorbance mechanism. The RCS of the proposed FSS is compared with the RCS of a reflective (metallic) sheet to analyze its suitability for practical applications (RCS reduction) within the working band. The 3D simulated and 2D calculated RCS results indicate that the proposed FSS is suitable for wideband EM wave absorber applications.

A Simple Overlapping DDM Preconditioned Fast HOVSIE for Wideband Scatterings of Anisotropic Medium-Metallic Objects

In this article, a fast high-order volume surface integral equation (HOVSIE) formulas solver will be presented to fast calculate the wideband electromagnetic (EM) scattering of anisotropic medium-metallic composite objects. First, in the HOVSIE, the equivalence volume and surface current vectors are discretized by the high-order hierarchical vector basis functions (HVBFs), which can reduce unknowns and facilitate the calculation of the broadband EM scattering. Second, a fast wideband algorithm, i.e., the hybrid multilevel accelerated Cartesian expansion–multilevel fast multipole algorithm (MLACE-MLFMA), is integrated to accelerate the matrix-vector multiplication in the iterative solution. Finally, in order to improve the iterative convergence, a simple overlapping domain decomposition method (ODDM)-based preconditioner is also employed in the proposed HOVSIE enhanced by the MLACE-MLFMA. Summarily, three advantages can be found here: 1) more flexible calculation of the wideband EM scattering; 2) less memory occupation; and 3) better iterative convergence. The accuracy, efficiency, and flexibility will be demonstrated in the numerical examples.

Achieving high temperature broadband electromagnetic reflection reduction via Al2O3 / FeCrAl refractory composite coating

Absorbing materials have gained great applications for the capability of electromagnetic (EM) reflection reduction. So far, it is still very challenging to simultaneously achieve high-temperature resistance and broad working band in one design. This work reports a composite coating to realize this goal by using refractory Al2O3 coating and high-temperature conductive FeCrAl by atmospheric plasma spraying (APS). The reflection reduction mechanism is the phase cancellation instead of absorption. By spraying the FeCrAl structure on the surface of Al2O3 coating, it can behave as resonators to produce a phase difference. Here, with a thin thickness of 1.7 mm, the composite coating shows stable wideband EM reflection reduction from room temperature up to 700 °C, which originates from the excellent conductivity of FeCrAl and the steady dielectric property of Al2O3. In addition, a protective layer is employed to isolate the contact between the structural layer and the outside high-temperature environment, which prevents the conductive structure from corrosion and greatly enhances the practicability and feasibility for daily maintaining. Sample characterizations show that these layers are prepared of low porosity and closely bonded to form the composite coating. The EDX mapping scan results and microstructure analysis demonstrate that the composite coating can exhibit excellent stability at high temperatures. Meanwhile, XRD results at different temperatures indicate the phase structure of Al2O3 coating is not damaged. This study provides a route to achieve temperature insensitive EM reflection reduction over a wide frequency range and enlighten a promising future of this material system.

Lightweight and Highly Compressible Expandable Polymer Microsphere/Silver Nanowire Composites for Wideband Electromagnetic Interference Shielding.

The exploration of lightweight and compressible electromagnetic interference (EMI) shielding materials with outstanding shielding effectiveness (SE) is still a tremendous challenge in the elimination of electromagnetic pollution. Lightweight and highly compressible expandable polymer microsphere/silver nanowire (EPM/AgNW) composites with micron-sized closed pores and an interfacial AgNW conductive network are fabricated via a facile thermal expansion process in an enclosed space. The EPM/AgNW composites with AgNW loading of 0.127 vol % show low density (0.061 g/cm3), high compressibility and compression strength (4.25 MPa at 92.6% of compressive strain), and high EMI SE (over 40 dB, 1 mm) at a wideband of 8-40 GHz. Their EMI SE can be improved to a record 111.5 dB by increasing the AgNW content to 0.340 vol %, which corresponds to the surface-specific SE (SSE/d; SE divided by density and thickness) up to 13433 dB·cm2/g. The EMI shielding mechanism is further discussed using the finite-element analysis software COMSOL Multiphysics, and the application of the EPM/AgNW composites is visually demonstrated via near-field shielding in a practical antenna radiation. The overall properties of light weight, high elasticity, excellent mechanical strength, and outstanding EMI shielding performance suggest that the as-prepared EPM/AgNW composites have a great potential for applications in modern electronics.

Biomass-Derived Carbon Heterostructures Enable Environmentally Adaptive Wideband Electromagnetic Wave Absorbers

HighlightsA novel, non-porous carbon structure was obtained through pyrolysis of biomass heterostructures consisting of cellulose and lignin.The novel class of biomass-derived carbon materials exhibit an enhanced electromagnetic (EM) loss capability due to the nano-antenna structure created by in-situ growth of carbon nanofibers on carbon nanosheets.The designed carbon materials exhibit good hydrophobicity and acid/base resistance, suggesting a stable EM absorption performance in diverse environmental conditions, thus making it a good candidate for real world conditions.

High-Yield Two-Dimensional Metal-Organic Framework Derivatives for Wideband Electromagnetic Wave Absorption.

Two-dimensional metal-organic frameworks (2D-MOFs) and their derivatives are promising for catalysis, energy storage, gas separation, etc. due to their unique microstructure and physicochemical properties. Many efforts have been devoted to fabricating 2D-MOFs with challenges remaining in yield and fine control of their thickness and lateral size. Here a versatile strategy has been used involving epitaxial, anisotropic, and confined growth of CoNi-MOF-71 nanosheet arrays, giving rise to excellent quantity and controllability of the 2D-MOFs. Electromagnetic (EM) wave absorption performance has been investigated for the resultant 2D Co/Ni/C derivatives. Compared with the bulk counterpart, significantly increased surface area, conductivity, and shape anisotropy for the 2D derivatives result in enhanced interfacial polarization, conductive loss, and magnetic resonance. As such, optimum EM wave absorption of minimum reflection loss RLmin = -49.8 dB and an ultrawide effective adsorption bandwidth EAB = 7.6 GHz can be achieved at a thickness of 2.6 mm. This work not only sheds light on the performance enhancement for 2D absorbers via synergistic effects of multiple attenuation mechanisms but also provides an effective fabrication route of ultrathin MOFs with high yield and uniform size for extended applications in catalysis, electrochemistry, and optoelectronics fields.

Hierarchical porous hollow graphitized carbon@MoS2 with wideband EM dissipation capability

Core-shell materials are promising broadband electromagnetic (EM) absorption materials since the highly component manipulation performance, interfacial effect etc. Herein, a well-defined core-shell shaped structure constructed by 2-dimensional MoS2 nanosheets-coated porous hollow carbon has been successfully designed with controlled pore-sizes of the core, adjustable shell content, and structure. By effectively optimizing the parameters for these factors, the as-prepared hierarchical porous hollow C@MoS2 sample enables an ultra-width EM absorption ability (covering 11.4–18.0 GHz) at a thickness of only 2.0 mm. The detailed contributions of each component and structure on the excellent EM absorption capability have been investigated. These encouraging results indicate that the development of core-shell composites with multiple controllable physical factors is of great significance for the future ultra-wideband electromagnetic absorbers.

Controllable synthesis of Ni-dotted Fe3S4 with its superior wideband electromagnetic absorbing performance

Transition metal dichalcogenides (TMD) have attracted considerable attention as promising electromagnetic (EM) absorbing materials due to the desirable conductivity loss ability. However, the single conductivity loss ability is still difficult to obtain high EM absorption performance. In this work, a Ni-dotted magnetic Fe3S4 nanoparticle has been produced via a simple solvothermal and subsequent ball-milling route. The results revealed that the Ni-dotted Fe3S4 is not only having conductivity loss, but also shows magnetic and polarization loss capability. Because of multiple loss mechanism, the Ni-dotted Fe3S4 shows wideband EM absorbing ability, with an effective absorption region of 6.4 GHz at a thinner thickness of 1.6 mm. Utilization of doping strategy to modify TMD material can be a candidate for producing high-performance EM absorbers.